AC can't keep house 75F in middle of 95Fsummer

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  #1  
Old 03-04-07, 02:17 PM
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AC can't keep house 75F in middle of 95Fsummer

AC can't keep house 75F in middle of 95F summer. House is 1750 sf. 1978. 10 yr old Trane 3ton 1200cfm unit with three trunks and four 7" and three 8" round metal duct vents. Trunks and plenum are insulated. No big windows facing south. 2 triangular gable vents and 2 12" turbines for attic ventilation. Attic space with garage is 2000 sf. Blown fiberglass insulation in attic is 10" high, except garage.

What are the best things I can do so AC can get house to 75F or below in the middle of the summer and keep it there for a reasonable amount of time?
 
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  #2  
Old 03-04-07, 04:04 PM
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The unit should be able to keep that space at that temp, pretty easy. If this is not happening then the unit is not working properly.
 
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Old 03-04-07, 04:09 PM
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Don't know how unit was sized! It could be sized for 90 degree days! Or 75 inside temp on 95 outside. Have to run a heat load on your home to find out! 20 degrees is about what it should be doing! Has the unit be serviced yearly?
 
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Old 03-04-07, 04:13 PM
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The 20 degrees is the "split" that you should get between your return and supply air.
This info helps us figure out how good the unit is cooling/heating.
 
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Old 03-04-07, 05:55 PM
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How's the coil outside? Has that been cleaned up over th years?

You have anyone out there to check the charge?

I don't know where you are out of, but I have 2 tons, and keeps up well with my 1700sq ft home.
 
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Old 03-05-07, 09:47 AM
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Originally Posted by azAir View Post
The 20 degrees is the "split" that you should get between your return and supply air.
This info helps us figure out how good the unit is cooling/heating.
That might make a difference. The house is normally 10F hotter inside than outside. So outside temp of 95 would mean an inside temp of 105. Not that it reaches 105 or even 95 but it would w/o AC and that is that temp is what the AC has to go against.
 
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Old 03-05-07, 09:47 AM
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Originally Posted by airman.1994 View Post
Don't know how unit was sized! It could be sized for 90 degree days! Or 75 inside temp on 95 outside. Have to run a heat load on your home to find out! 20 degrees is about what it should be doing! Has the unit be serviced yearly?
I will have a heat load done. Thanks.
 
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Old 03-05-07, 09:56 AM
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Originally Posted by Jay11J View Post
How's the coil outside? Has that been cleaned up over th years?

You have anyone out there to check the charge?

I don't know where you are out of, but I have 2 tons, and keeps up well with my 1700sq ft home.
The charge is good. It had a leak last summer that was fixed. Even with the leak the AC was running good on warm days, until almost all of the freon leaked out. Where is the best AC maintenance guide.
 
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Old 03-05-07, 04:47 PM
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What did the paper work say it would hold the inside temp down from the outside temp most say just 15o is all.
 
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Old 03-06-07, 09:26 AM
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Originally Posted by Ed Imeduc View Post
What did the paper work say it would hold the inside temp down from the outside temp most say just 15o is all.
It doesn't say. It says "Set the temperatures by using the indicators on the thermostat control. After that, your thermostat will maintain a constant indoor termperature, regardless of changes in outdoor temperatures."

I wish that was true.
 
  #11  
Old 03-06-07, 06:19 PM
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Originally Posted by dvasco View Post
It doesn't say. It says "Set the temperatures by using the indicators on the thermostat control. After that, your thermostat will maintain a constant indoor termperature, regardless of changes in outdoor temperatures."

I wish that was true.
Yeah me too. Here in florida, that doesnt happen. Especially in my apartment, which has no insulation in the walls, the living room is always warmer then anywhere else in the house.

Most people usually dont keep their houses lower than 78 or so when it is that hot out, so house builders and AC manufacturers don't design them for that.

The only way to do that now is to get a bigger unit, but that would mean more money.
 
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Old 03-06-07, 06:57 PM
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I think your missing the point - the "split" I'm referring to is in the inside, Return air temp vs the supply air temp. With clean coils and proper air flow u should get this. The outside temp will start reducing this split as it get hotter. try feeling the large line after it has been running for a while. It should be cold, beer can cold. I really think u are just low on charge.
 
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Old 03-06-07, 07:27 PM
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I skimmed through the posts quickly. Did anyone ask what kind of temp he gets out of a register from his a/c? Even though there is the "rise" factor form differential in temp, I always find when checking register temps on houses and condos that they are around the low-mid 50's at a nearby register to the furnace. Even the commercial building I took care of with those heat pumps had those temps at the registers.

If he is low on charge...if his temp at the register is say 70...it takes till the cows come home to bring the house temp down, even if that temp is below the desired temp (by 5 degres in his case). You need the register temp to be WAY colder than the desired temp for the house to drop fairly quickly without running a up a big compressor tab ($) for nothing.
 
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Old 03-06-07, 08:49 PM
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Originally Posted by azAir View Post
I think your missing the point - the "split" I'm referring to is in the inside, Return air temp vs the supply air temp. With clean coils and proper air flow u should get this. The outside temp will start reducing this split as it get hotter. try feeling the large line after it has been running for a while. It should be cold, beer can cold. I really think u are just low on charge.
I understood, I worded my response incorrectly. What I was thinking is that maybe the split is 20 degrees but that as soon as the air exits the vent it is heated up 20 degrees too quickly. Meaning the supply air temp is staying constant and the AC can't keep up.

I still need to do a lot of things mentioned by you and others before it can be narrowed down. I haven't had time to check anything since those suggestions were made. The weather has been nice lately. One more month and it will be hot and then I can check temps at the supply, return, and at the vents. And I can check the cold line. Tomorrow I will check the coils. When the leak was repaired in March 2006 I know the repairman looked at the outside unit. No cleaning was necessary at the time. Hopefully that was clean enough for most of the summer.

I did have time to look at the receipts for the leak. The leak started July 2005. System was recharged with 4lbs of R-22, but the leak was not attempted to be located. The guy wanted to sell me a new system. The AC ran ok until Nov 3, 2005. Winter was around the corner so waited until spring. I had the leak repaired March 6, 2006 and system recharged. The AC ran ok until it got very hot out, but the line never froze like it did with the leak. I wish I had known about this forum back then.
 

Last edited by dvasco; 03-06-07 at 09:16 PM.
  #15  
Old 08-05-07, 05:46 PM
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Unhappy Its happening again - What do I do?

It's 102 on the thermometer on the porch.
The thermostat is set to 75 and has been for 1.5 hours, was set to 79, but it shows the actual temp to be at 80 at the thermostat.
The thermometer in the return at the ac unit in the house is 75
The same thermometer at a vent is 60
Is this the split? 15 ?
I never checked this when it was 90-95 so I don't know if I had a larger split then.
The outside unit looks very clean when I inspect it with through the vents. I haven't pressured washed it though so maybe it has some dirt in not immediatly visible.
This is my unit by the way -
http://www.bigtexair.com/products/xe1200/xe1200_page2.htm

BTW, the line at the compressor is beer can cold.
 
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Old 08-05-07, 06:41 PM
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AC can't keep house 75F in middle of 95Fsummer

Basing your measurements on a system that has only be set at 75 degres for 1.5 hours may not tell you much.

That is not enough time to cool down the walls, floors and furniture or to remove much humidity. - You may get different numbers after it has run for a day.
 
  #17  
Old 08-05-07, 07:30 PM
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60 degrees is really not cool enough to keep the house at 75 when it is that hot out. No matter how hot out it is the register temperatures should always in the low to mid 50s when the system is properly charged.

Also, 1.5 hours is not nearly enough to lower the temperature 4 degrees. It can take like 6 hours because the more heat that builds up in the house, the longer it takes to remove it. Let it run for a day like the previous post said.
 
  #18  
Old 08-05-07, 08:22 PM
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Red face

Ok, I didn't know the register temperatures should be in the low to mid 50s when the system is properly charged. I guess I'll have to get someone out to properly charge the system. In the meantime I'll make sure my wife doesn't raise the thermostat in the day again while I am at work.
 
  #19  
Old 08-05-07, 08:36 PM
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You want to check the temp over the coil at the coil. A 16o to 18o drop over thee coil is good. Might also check the big copper line it should be cold and wet the small copper line warm to hot at the outdoor unit. Dont play with the tstat let it set. Most companys say that they will give you a 15o drop some say 20o from the outside temp is all
 
  #20  
Old 08-18-07, 07:11 PM
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Solutions found

An AC repairman came out and checked the Freon charge, took temp readings, checked the amperage, and cleaned the outside coil. He coincidentally was the person that had installed the system for the previous homeowner 13 years ago. He said the charge was good and more would be too much. That means the person that fixed the leak and recharged the system did a good job. The compressor was pulling 14 amps and max was 17 amps. The temps were the same as I had reported before. 75F at the return and 60F at the closest vent. He said that I am not going to get 50F unless it is 65F at the intake and that at 100F I am getting 3 tons of heat and 3ton system is pulling 3tons of heat. He said the 3ton system was meant for my size house but also said systems in our area are sized at 1ton for every 500 sf. At 1750 sf I should have a 3.5 ton system. So I asked him about that and said that the only time I need that size is when it is 100F and that the solution since a few years ago is a two-stage 4ton system. I had never heard of them and he explained that they run 60% at 85F, which is 2.4 tons and 100% at 100F which is 4tons and what I think I need in 95-105F heat. I wish I had the money for a two-stage system. BTW, once the coil was cleaned it didn't really make a difference even the next 2 days.
Therefore the best advice I have had in this thread is to run the system at a lower temp from the morning which has helped the system stay a bit ahead of the heat.
 
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